I.J. Martin, R. Casalini
Naval Research Laboratory,
Keywords: azobenzene, networks, ionomers,
Summary:Soft materials that exhibit viscosity control by external stimulus are a critical need in the development of 3D printable elastomers for additive manufacturing (AM). The goal of this project is to develop novel, viscosity-controlled ionic polymers that can be further chemically crosslinked to form ionic-covalent double networks (icDNs). Functionalizing the ionic polymers with azobenzene (AB) will provide a photo-triggered handle for viscosity control based on known effects of AB cis↔trans isomerization on the bulk properties of polymeric materials. The AB-containing ionic polymers will be prepared from a low molecular weight, low glass-transition temperature prepolymer capable of chemical crosslinking. This affords the necessary low viscosity for AM while still permitting chemical network formation. Physical crosslinking will occur through interchain complexation of ionized pendant AB groups and a small addition of a metal cation. This enables the “toggling” of physical network formation, and ultimately viscosity, by “light”. In total, this provides a low viscosity prepolymer during AM, high viscosity transformation upon blue light irradiation, and finally icDN formation by chemical crosslinking. This class of materials will have potential applications for a broad range of applications such as smart materials and artificial muscles.